Project Summary/Abstract Neurodegenerative diseases represent an ever-increasing societal and economic burden with WHO estimates indicating that they will replace cancer as the 2nd leading cause of death by 2040. In neurodegenerative disease research, a wealth of pathways has been uncovered, but their direct and primary relevance to the respective human disease has been difficult to prove and targeting of pathways has remained difficult. The proposed work will characterize ATXN2 and pathways regulated by ATXN2 as therapeutic targets for amyotrophic lateral sclerosis (ALS), a disease burdening 1 out of 25,000 individuals. The ATXN2 gene is mutated in spinocerebellar ataxia type 2 (SCA2), a hereditary neurodegenerative disease affecting cerebellar Purkinje cells (PCs) and other neurons in the cerebellum and brainstem. Studies by us and others have demonstratedthat long normal CAG-repeat expansions in ATXN2 significantly increase the risk of ALS. More recently, survival (or lifespan) of some ALS mouse models and cultured ALS neuronal models were shown to be modified in association with ATXN2 mutation or overall level of expression. ATXN2 functions in mRNA metabolism based on its interactions with multiple RNA binding proteins (RBPs) including A2BP1/RBFOX1, DDX6, PABP1, and the ALS proteins TDP-43, FUS. Our most recent data demonstrate that mutant ATXN2 interacts with the stress granule (SG) RNA interacting protein Staufen1, and that this interaction has specific downstream effects on SGs. Since ALS motor neurons are also characterized by RNA granules, ATXN2 functions regulating staufen positive RNA granules in motor neurons may be relevant to ALS. The objective of this grant is to investigate ATXN2 as a therapeutic target for ALS using human pluripotent stem-cell-derived motor neurons from ALS and SCA2 patients. Three specific aims are proposed: 1) We will perform gene editing a panel of pluripotent stem cell lines (?CRISPR editing?) creating multiple pairs of cells that are genetically identical (?isogenic?) except for the edited change at of the ATXN2 gene. 2) We will then extensively characterize the phenotype of these cells vs ALS cells when differentiated to motor neurons neurons. 3) We will determine how lowering the expression of ATXN2 using our existing ATXN2 antisense oligonucleotide DNA drug alters the phenotypes of patient motor neurons generated in aim 1, including the dynamics of RNA granules in the presence of ATXN2 mutation. The proposed work will clarify the role for SGs in neurodegeneration and will aid in the identification of new avenues toward treatments of ALS and other degenerative ataxias including SCA2.